Inspection and testing (NDT and destructive testing)
The exam tests method selection, the governing standard, timing of inspection, and acceptance levels.
Core rules
- Surface methods: VT to ISO 17637, PT to ISO 3452 series, MT to ISO 17638. MT works only on ferromagnetic material.
- Volumetric methods: RT to ISO 17636-1 (film) or -2 (digital), UT to ISO 17640; phased array to ISO 13588, TOFD to ISO 10863.
- Acceptance: ISO 5817 for steel and ISO 10042 for aluminium, quality levels B, C, D. ISO 17635 links quality level to method and extent.
- Timing: for crack-susceptible steels, delayed inspection (commonly 24–48 h after completion) lets hydrogen cracks open.
- Destructive tests from ISO 15614-1: cross-weld tensile, 180° bend over a 4t former, Charpy impact, hardness to ISO 6507-1, macro to ISO 17639.
Worked example
A toe crack is reported on a 304L nozzle. MT is the wrong tool: 304L is austenitic and non-ferromagnetic, so it would give no meaningful indication whatever the defect. Use PT for the surface-breaking crack; if depth is required, use UT with a technique suited to coarse austenitic grain, such as a dual-element or TRL probe. RT is weak on tight, planar, misoriented cracks.
Traps
Specifying MT on stainless; treating a PT indication as a depth measurement; quoting RT capability without the IQI class; accepting UT reports missing frequency, angle and reference block; relying on one method for planar defects.